Sail offers a number of advantages over powered ships, including the freedom from requiring fuel bunkers and costs. In a post-carbon world, among the options for shipping is a return to the use of wind power for at least a significant portion of shipping (and the elimination of 1/3 of hulls and cargoes presently comprised of petroleum shipments).
John Michael Greer looked at this in a recent post on Captain Gustaf Erikson, who maintained a fleet of commercially-operating windjammers through the mid 20th century, particularly with steel hulls and wire rigging.
It's also why you'll find navies at the forefront of research on energy research and propulsion. There have been three major revolutions in marine propulsion over the past two centuries: the emergence of coal in the 1850s (much later than its use in shorter-haul shipping and railroads due to the need to establish coaling stations -- an accomplishment demonstrated by the voyage Great White Fleet in 1907-1909), oil starting just prior to WWI, when Admiral of the British Navy Winston Churchill converted its fleet, and nuclear energy following WWII under US Navy Rear Admiral Hyman Rickover, though the latter propulsion was adopted only for aircraft carriers, submarines, and icebreakers, with the exception of a very few other experimental nuclear powered vessels.
Navies are at the forefront of current research into next-generation fuel sources given the dual challenges of peak oil and global warming.